This invention relates to the preparation of aromatic esters by the catalyzed oxyacylation reaction of benzene or aryl alkyl compounds, oxygen and a carboxylic acid in the vapor phase.
The preparation of aromatic esters by the vapor phase reaction of an aromatic compound, carboxylic acid and oxygen in the presence of a noble metal containing catalyst, especially palladium, is well-known. Thus, for example, with acetic acid, when using benzene, phenyl acetate is obtained, and when using toluene, benzyl acetate is prepared. U.S. Pat. No. 3,275,680 granted to Holzrichter et al. discloses such a reaction and is hereby incorporated by reference.
Over the years, the oxyacylation reaction has been the subject of an extensive research effort because, for one reason, the noble metal catalyst is very expensive and it is an important cost factor in the process. U.S. Pat. No. 3,275,680, Great Britain Pat. Nos. 1,017,938 and 1,117,595 each describe the preparation of benzyl acetate and other benzyl esters wherein an alkyl-substituted phenyl compound such as toluene is reacted in the gaseous phase with an oxygen containing gas, for example, air, acetic acid, and an alkali metal acetate in the presence of a catalyzst containing palladium metal supported upon a suitable substrate. Candian Pat. No. 820,352 describes a similar process wherein the catalyst contains metallic palladium and gold, and an alkali metal salt as sodium acetate. Great Britain Pat. No. 1,328,058 describes a process for preparing benzyl acetate by the reaction of toluene, oxygen and acetic acid in the gaseous phase at an elevated temperature in the presence of a supported catalyst system containing an oxide, hydroxide or carboxylate of palladium and bismuth, or in the case of palladium, the metal itself, and a hydroxide, carbonate or carboxylate of an alkali metal compound. Other metals, including gold and/or copper, or compounds of these metals which do not contain halogen, sulfur or nitrogen, may be added so as to affect the activity and selectivity of the catalyst.
It has now been found that benzene, toluene and other aryl alkyl compounds may be catalytically oxyacylated to phenyl acetate, benzyl acetate and other such esters without the need for using a noble metal catalyst.
It is an object of this invention to provide an improved oxyacylation process for the preparation of aromatic esters from benzene or aryl alkyl compounds. Other objects and advantages will become apparent from the following description.